1. Field of the Invention
The present invention relates to a piston for a hydraulic brake, which is manufactured in forming processes from a metallic base material, in particular from plane sheet metal, and is configured as a bowl, open on one side, with a longitudinal axis, a wall and a bottom, and is delimited on an open end face by a rim with an axial abutment surface which is movable into abutment on a brake pad.
2. Description of the Related Art
WO 01/02745 A1 discloses a piston of this type. The piston is a cold-worked piston which is preferably made in a deepdrawing process. Compared to cast pistons, the above piston is comparatively thin-walled, and the base material, the wall and the bottom have the same thin wall thickness. In order to prevent the bottom from deforming when pressurized pressure fluid is applied to it, it has a convex curvature with regard to a piston outside surface, with the result that the stress causes compressive strain in the bottom. Due to this stabilizing constructive design of the bottom, a large clearance volume develops between piston and an associated brake cylinder. Furthermore, the forces that act on the bottom are transmitted into the wall of the piston, and increased stress is produced in a transition area between bottom and wall. To compensate the stress, the material is folded several times at this point. It proves being advantageous in this respect that the folding of the material is particularly complicated in terms of the configuration and cost-intensive, especially as regards the manufacturing tool.
EP 1 414 613 B1 discloses a method of manufacturing a piston for a hydraulic brake comprising the following steps: punching out a disc-shaped round blank from a base material of defined thickness, especially a piece of sheet metal, forming the blank into a bowl-type hollow cylinder by means of a press die and a stamp, and compression molding of the bowl-type hollow cylinder for forming the bottom with a defined wall thickness and a cylindrical wall with a defined wall thickness. As a result of the forming process executed, the wall thickness of the piston is greatly reduced compared to the base material, in particular in the transition of bottom and wall. To achieve a sufficient rate of piston wall thickness, i.e. stability and rigidity, it is required to choose a comparatively thick base material, with higher manufacturing costs being hereby incurred.